Plants for the treatment of bodyworks

ABSTRACT

A plant for treatment of bodyworks may include: at least one trolley configured to support a bodywork to be treated; a conveying line configured to transport the at least one trolley along the plant; a first system configured to move the at least one trolley along the conveying line; a second system configured to move the at least one trolley along the conveying line; and sensors configured to detect angular position of a toothed traction wheel and approaching movement of the at least one trolley toward the toothed traction wheel. The at least one trolley may include a traction rack extending in a direction of movement of the at least one trolley along the conveying line in at least one zone of the plant. The toothed traction wheel may be configured to engage the traction rack upon passage of the at least one trolley into the at least one zone.

The present invention relates to a plant for the treatment of bodywork,in particular for motor vehicles and the like and to an operatingmethod.

In the art treatment plants which comprise conveyor lines fortransporting a plurality of trolleys, for example in the form of slidingunits or skids, each comprising a bodywork to be treated, are known.

For example treatments which involve the immersion of the bodywork inspecial basins filled with treatment liquid, for example for performinganti-corrosion and electrophoresis pre-treatments, are known. Theseplants have, arranged opposite the basins, immersion systems which forexample rotate the bodywork on the trolley so that it can be immersed inthe basin and then extracted.

It has been noted that in some points of the plant the trolley mayrequire an additional thrust to overcome particular resistance to theadvancing movement. For example, in immersion systems with rotation ofthe bodywork, the rotating movement may require a temporary increase inthe advancing force of the trolley. For example, this may be caused byan imbalance in the weight of the bodywork on the trolley with respectto the axis of rotation. In particular, immersion systems which obtainthe rotational force from the advancing movement itself of the trolleyare known. For example, such a rotation system has been proposed in thepatent EP3237314. In this document it was also proposed using additionaltraction systems consisting of a motorized wheel which rests withfriction on a longitudinal surface of the trolley and helps thetransportation system to push the trolley forwards during rotation ofthe bodywork.

The use of a friction wheel has, however, a fairly low limit value ofthe tractional force which the wheel may apply to the trolley and,especially in particularly demanding applications (for exampleparticularly heavy bodywork which must be rotated), the wheel in someconditions may slip on the surface of the trolley. The torque which canbe transmitted by the wheel may also decrease significantly owing to thedirt or liquid between the surfaces making contact. Moreover, the wheelmay be subject to a relatively high degree of wear and this may resultin a further reduction in the traction which can be imparted by thewheel on the trolley and the production of waste matter which maycontaminate the bodywork treatment basins. Attempts have also been madeto improve the adhesion of the wheel by increasing the force with whichit is pushed against the surface of the trolley, but this system worsensfurther the wear and continues in any case to have a relatively lowlimit value of the torque which can be transmitted before slipping ofthe wheel occurs.

The object of the present invention is to provide a plant and a methodwhich solves the aforementioned problems of the prior art.

In view of this object the idea which has occurred, according to theinvention, is to provide a plant for the treatment of bodywork,comprising at least one trolley designed to support a bodywork to betreated, a conveyor line for transporting the trolley along the plantand with a first system for moving the trolleys along the conveyingline, characterized in that the trolley comprises a traction rackextending in the direction of movement of the trolley along theconveying line and, in at least one zone of the plant, there is atoothed traction wheel which is driven by a motor controlled by a motorcontrol system and which is adapted to engage in the traction rack uponpassage of the trolley into this zone so as to move the trolley along aportion of the conveying line under the control of the motor controlsystem and provide a second movement system for the trolleys, therebeing also sensors designed to detect the angular position of thetraction wheel and the approaching movement of a trolley towards thiswheel and connected to the motor control system of the toothed wheel soas to cause the engagement between the traction rack and the toothedtraction wheel upon arrival of the trolley.

Still according to the invention the idea which has occurred is toprovide a method for providing an additional traction to trolleys fortransporting bodywork in zones along a line for conveying the trolleysin a plant for treating such bodywork, comprising the steps of providingon the trolleys a traction rack extending in the direction of movementof the trolleys along the conveying line, arranging in said zones alongthe conveying line a toothed traction wheel which is driven by a motorcontrolled by a motor control system and which is able to engage in thetraction rack when the trolley passes into said zone so as to move thetrolley along a portion of the conveying line under the control of themotor control system, arranging sensors designed to detect the angularposition of the traction wheel and the approach movement of a trolleytowards said wheel and connected to the motor control system of thetoothed traction wheel, and the further steps of detecting the angularposition of the toothed traction wheel and, when the toothed tractionwheel is not engaged in the traction rack, driving the motor so as tobring this wheel into a given position suitable for subsequentengagement with the traction rack of an inbound trolley, detecting thearrival of a trolley and starting the motor with a predeterminedacceleration ramp when the front end of the traction rack approaches thetoothed traction wheel until the toothed traction wheel and the tractionrack are engaged and driving the motor so as to continue the rotation ofthe toothed traction wheel for a pushing action of the trolley along theconveying line by means of the traction rack engaged in the toothedtraction wheel.

In order to illustrate more clearly the innovative principles of thepresent invention and its advantages compared to the prior art, anexample of embodiment applying these principles will be described belowwith the aid of the accompanying drawings. In the drawings:

FIG. 1 shows a schematic side elevation view of a part of a plantdesigned according to the invention;

FIG. 2 shows a schematic view of the plant cross-sectioned along theline II-II of FIG. 1;

FIG. 3 shows a schematic view, on a larger scale, of the plantcross-sectioned along the line III-III of FIG. 1;

FIG. 4 shows a schematic view similar to the cross-section of FIG. 3 andwith a further device of a plant according to the invention;

FIGS. 5, 6 and 7 show two different operating steps along the plantaccording to the invention;

FIG. 8 shows in schematic form a part of a plant according to theinvention during various possible operating steps.

With reference to the figures, FIG. 1 shows in schematic form a firstexample of a part of a plant, denoted overall by 10, applying theprinciples of the present invention.

The plant 10 comprises at least one means of transport for a bodywork,which is here generally referred to as a trolley 11 (for example it maybe a sliding unit or skid or an actual wheeled trolley) intended tosupport a bodywork 12 to be treated. Usually the trolleys will consistof a plurality and will travel along the plant in sequence so as to eachtransport a bodywork to be treated into the various treatment stations.

The plant 10 also comprises a conveying line 13 for the sequentialtransportation of the trolleys along the plant.

As will be clarified below, the plant comprises at least one firstsystem for moving the trolleys along the conveying line.

The conveying line may comprise, for example, travelways, arrangedparallel, for supporting side elements 14 of the trolley, such asrunners and/or wheels, and the advancing movement may he produced forexample by a series of motorized rollers on which the trolleys restand/or by other known motorized movement means, as may be easilyimagined by the person skilled in the art.

As can he clearly seen in FIG. 2, the trolleys may comprise, forexample, lateral support elements 14 formed for example on one side byof a lateral runner 14 a and on the other side by one or more wheels 14b. The runner 14 a may rest on one side of the conveying line 13, forexample formed with rollers 13 a, while the wheel 14 b may rest on asliding surface or track 13 b.

Those rollers of the conveying line which may be motorized may be allconnected to a single motor, for example by means of a chain system, asmay be easily imagined by the person skilled in the art.

Other known systems for normal transportation of the trolleys along theline 13 may in any case be used, as may be easily imagined by the personskilled in the art on the basis of the description provided here.

Different sections of the conveying system may also be motorizedseparately and/or use different systems for moving the trolleys in orderto obtain for example asynchronous transportation of trolleys which maythus be moved at different speeds and/or stop along the varioussections.

The plant 10 also comprises at least one known process liquid basin 15inside which the bodywork must he immersed, for example for ananti-corrosion and electrophoresis pre-treatment. Below reference willbe made to a basin, but it is understood that the basins may consist ofa plurality along the plant, also depending on the number and type oftreatments required, as will be evident to the person skilled in theart.

The trolley 11 described here advantageously comprises a base part 16for sliding along the conveyor line and a part 17 which supports thebodywork and is rotatable about an axis 18 of a rotatable shaft 19supported by the base part. Preferably, the axis 18 may be transverse tothe direction of movement, even though other arrangements (for example alongitudinal or inclined arrangement) may be used.

With reference to FIG. 2, the base frame of the trolley may comprise,for example on one side, the runner 14 a, a central crossbeam whichcomprises or is formed by the rotatable shaft 19 and its correspondingsupport elements on the frame, and an opposite support point at theother end of the shaft formed for example by a wheel 14 b. The base partmay thus have advantageously a generally T-shaped form in plan view.Alternatively, the base part could in any case have an H-shaped framewith longitudinal runners on both sides. In any case, the lateralsupport points of the base part 16 of the trolley on the conveyingsystem 13 are advantageously situated on the outside of the sides of thebasins 15.

As can be clearly seen in FIG. 1. the top part 17 of the trolley maycomprise one or more support elements 17 a which extend from therotatable shaft 19 so as to support and lock the bodywork to the shaftby means of known fixing means, optionally via a support surface orframe 21 (omitted for easier comprehension in FIG. 2). Advantageously,in the normal transportation position shown in FIG. 1 the supportelements are directed upwards above the rotatable shaft 19.

The trolley 11 shown in the figures also comprises a mechanism 22 forthe controlled rotation of the shaft 19 which allows the bodywork to bemoved between a normal advancing position, as shown in FIG. 1, and anoverturned position for immersion inside a basin 15, which is shown forexample in FIG. 7.

The plant 10 also comprises a device 32 for actuating the rotation ofthe shaft 19. This device is advantageously located in each zone alongthe plant where it is required to perform the controlled rotation of thebody about the axis 18 of a trolley.

Advantageously, the rotation mechanism 22 comprises a toothed actuatingwheel 23 kinematically connected to the shaft 19, optionally via atransmission assembly 24 known per se with a suitable transmissionratio. Preferably, the transmission between wheel 23 and shaft 19 willbe such that the wheel 23 and the shaft 19 rotate in the same direction.However, an opposite direction of rotation may also be used, ifrequired. The transmission ratio may be preferably chosen so as to geardown the number of revolutions in order to reduce the force on therotation actuation device and on the advancing movement system.Moreover, the transmission ratio may be chosen so as to define a desiredspeed of rotation in relation to the speed of advancing movement and/orthe number of teeth (rollers) of the rack.

As can be clearly seen in the figures, the device 32 comprisesadvantageously a rotation rack 33 which is arranged along the directionof movement of the trolleys along the conveying line 13.

The rack 33 will have a form suitable for engagement with the toothedwheel 23 so as to rotate the toothed wheel 23 by means of the movementitself of the trolley along the conveying line.

The trolley may advantageously also support a device 27 forlocking/unlocking the free rotation of the shaft 10 so that the bodyworkdoes not rotate uncontrollably, for example when the wheel 23 is notengaged. with a rack 33.

The device 27 may for example act on the toothed actuating wheel 23 soas to block the rotation thereof For example it may he of the mechanicaltype formed by a frame 28 hingeably mounted on the trolley and providedwith an engaging element 30 and an actuating shoe 31. In the restcondition, the engaging element 30 is engaged with the wheel 23 so as tolock it, while a suitable operating surface along the trolley conveyingpath may act on the shoe 31 so as to move the frame 28, thus raising theshoe and disengaging the engaging element 30 from the toothed Wheel 23when required.

In the normal condition for conveying along the line, there is nointerference with the shoe 31 and the trolley is able to continueconveying the bodywork in the upper position, while in the zones wherethe rotation of the bodywork on the trolley is to be released, it ismerely required to provide suitable surfaces for operation of the shoe.

In particular, an operating surface may be associated with the device 32for actuating the rotation of the trolley so that the wheel is releasedwhen it must be operated by this device 32. Advantageously, as shown inthe figures, the rack may be a roller rack and the wheel 23 may be awheel which is correspondingly lobed or a petal wheel for engagingsequentially with its lobes between the rollers. This ensures secure,reliable and relatively silent engagement. Moreover, the same rollers ofthe rack 33 may form the surface for raising the shoe 31. Alternatively,an independent surface for actuating the shoe may be provided in asuitable position, for example parallel to and alongside the rack.

The device 27 for locking; unlocking the wheel 23 ensures also that thewheel 23 comes up against the rotation rack 33 in the correct positionfor engagement with the teeth without jamming, then allowing rotationwhen the engagement is secure.

Advantageously the actuating device 32 may also be movable controllablybetween an operating position engaged in the wheel 23 and anon-operating position where the wheel may pass along the rack withoutengaging with it and without the locking/unlocking device for the wheel23 releasing the wheel. The movement of the actuating device 32 may beperformed for example using a motorized, hinged, parallelogram mechanism38 which, when operated, raises or lowers the rack so as to move itbetween the two operating and non-operating positions, as may now beeasily imagined by the person skilled in the art on the basis of FIG. 1.

If it is required for any reason to convey a trolley into the vicinityof an actuating device 32 without causing rotation thereof it is thussufficient to move the actuating device towards its non-operativeposition. For example, this may be useful in the case where there aresome types of bodywork which must be treated in some basins and otherbodywork which must be treated in other basins along the same conveyingline or in the case of maintenance activities which for example requirethe exclusion of one or more basins.

The plant 10 comprises according to the invention an additional tractionsystem 60 for providing, when desired, the trolleys with additionaltraction compared to the traction provided by the normal system forperforming transportation along the line. This additional systemtherefore provides a second system for moving the trolleys along theconveying line. In particular, when rotation of a bodywork on thetrolley must be performed, the weight itself of the rotating bodyworkmay result in the need for a thrust for displacing the trolley along theconveying line which is greater than that normally required for simplesliding of the trolley with the bodywork on the trolley in the normalconveying position. This is particularly necessary for example when therotation of the bodywork is performed by the same forwards movement ofthe trolley, as in the embodiment described above.

The additional traction system 60 comprises a toothed traction wheel 61driven by an electric motor 66 and a complementary traction rack 62arranged on the base body of the trolley and extending parallel to thedirection of movement of the trolley so as to engage in the toothedwheel 61 upon passage of the trolley into the zone where the additionaltraction is required. Advantageously, as can be clearly seen in FIG. 2,the rack 62 of the additional traction system may be placed on one sideof the trolley, for example above the sliding runner 14 a. As can heseen in the figures, the toothed traction wheel 61 may be for example awheel with petals or lobes and the rack may be a roller-type rack.

The system 60 also comprises a first sensor 63 for detecting the angularposition of the wheel 61 and a second sensor 64 for detecting theapproaching movement of the trolley (or in an equivalent manner of itstraction rack) towards the wheel 61. The sensors 63 and 64 are connectedto a control system or circuit 65 which controls the motor 66 forrotation of the toothed traction wheel 61. The control system 65 and thesensors 63, 64 form a synchronization system which allows the toothedwheel 61 to be engaged in the rack 62 while the trolley advances,avoiding any jamming.

In particular, the control circuit 65 receives the signals from the twosensors 63, 64 and causes rotation of the wheel 61 so as to synchronizeelectronically the wheel with the traction rack 62 so as to allow themto engage together without jamming, despite the sliding movement of thetrolley, before the engagement is activated by the other system fordriving the trolley along the conveying line. The control circuit 65 maybe a structure which is generally known per se for the systems foractuating an electric motor and the detection and processing of signalsfrom sensors (for example an electronic circuit formed with cabled logicand with a suitably programmed microprocessor system). It will thereforenot be further illustrated or described in detail here.

A synchronization method according to the invention, which may beimplemented in the control system 65, may envisage also the followingsteps:

Initially, when the toothed traction wheel 61 is not engaged in thetraction rack 62, the angular position of the toothed traction wheel 61is detected by means of the angular position sensor 63 and the motor 66is controlled so as to bring the wheel 61 into a given position suitablefor subsequent engagement with the traction rack 62 of an incomingtrolley. In particular, the wheel may be arranged with a recess betweentwo teeth directed towards the rack so as to receive the first roller ortooth thereof. The angular position sensor may be any known sensorsuitable for detecting the correct position of the wheel. For example,it may be an absolute encoder, a proximity sensor which controls atooth, etc. The sensor may also be incorporated in the motor or consistof the motor itself. For example, an absolute angular control motor maybe used.

Obviously it is not necessary to know exactly which recess (or tooth) isin the correct position, but it is sufficient to detect that the wheelis in the desired position suitable for subsequent engagement.

Preferably, once the traction wheel is positioned as a result of thesensor 63, the control circuit 65 stops the motor 66 and the wheel 61 isreleased (not braked).

The control system then waits for detection of arrival of a trolley andstarts the motor 66 with a predetermined acceleration ramp when thefront end of the traction rack 62 moves closer towards the toothedtraction wheel 61 until the toothed traction wheel and traction rackengage with each other.

The position sensor 64 may advantageously form part of a linearpositioning system such as a linear encoder. The position sensor 64 mayalso be a proximity sensor. When the trolley arrives, if there should bea small impact between rack and tooth this impact may in any case beabsorbed by the mechanical friction of the motor 61 (which willpreferably be a gear motor) which at the moment of impact will beadvantageously braked and have a low or zero operating torque.

At a given relative position of the rack and the petal wheel (calculatedby the system using the sensor 64) which establishes that engagement hasnow started, the motor 66 may be advantageously activated by means of agradual torque.

The rising torque curve is advantageously graduated so as to makeengagement as soft as possible, preventing excessive acceleration ordeceleration which could result in an anomalous force acting on thetrolley movement system which moves the trolley towards the engagementpoint.

After engagement, the motor 66 is controlled by the system 65 so as tocontinue with rotation of the toothed traction wheel 61 so as to movethe trolley along the conveying line by means of the traction rackengaged in the toothed traction wheel 61. The speed of movement of thetrolley will therefore be essentially governed by the control system bymeans of the motor 66. Essentially the start of the command for rotationof the motor 66 is determined by means of the position sensor 64 whichallows the circuit 65 to calculate when the front end of the tractionrack 62 comes up against the first tooth of the traction wheel,positioned correctly by means of the sensor 63.

Advantageously, the sensor 64 also allows the detection of the positionof the trolley which is at the end of the engaging operation or which isin any case close to the end of engagement of the additional tractionsystem. In this way, at the end of engagement, the motor 66 may be usedagain to position correctly the wheel 61 by means of the sensor 63 andwait for the arrival of the next trolley.

Obviously, even though the sensor 64 has been described as a singlesensor which may detect the position of the trolley which is close tothe start of engagement and the position of the trolley which is closeto the end of engagement, this sensor 64 may be composed of two sensorswhich each detect one of the two positions so as to communicate them tothe circuit 65, as may now be easily imagined by the person skilled inthe art.

Although the system 60 has been defined as an additional tractionsystem, this system 60 must be understood as being a system whichprovides a greater traction for the movement of the trolley and notnecessarily as a system which is in addition to the normal system formoving the trolleys along the conveying line 13. In particular, it maybe envisaged that the system which moves the trolley towards the pointfor engagement between the toothed traction wheel 61 and the tractionrack 63 is deactivated once the traction wheel 61 has engaged with thetraction rack 52 so that the task of moving the trolley is passed overentirely to the system 60. In the case where the use of the additionaltraction system is envisaged in order to favour the advancing movementduring the operations for rotating the body on the trolley, the relativeposition of the additional traction system composed of the tractionwheel 61 and rack 62 with respect to the rotation mechanism operated bythe shaft 19 may be such that the rotation system acts only afterengagement of the additional traction system has been completed. Inparticular with the rotation mechanism shown in the figures, the wheel61 is positioned with respect to the rack 33 for performing rotation ofthe shaft 19 so that engagement of the rotation wheel 23 on therespective actuating rack 33 occurs only after engagement of theadditional traction system has been completed. Similarly, advantageouslyengagement of the additional traction system terminates (namely thewheel 61 is disengaged from the respective rack 62) only after rotation,namely engagement between the wheel 23 and the respective rack 33, hasterminated.

Advantageously, it may also be envisaged that, in the zone whereengagement of the additional traction system must be performed, movementsystems with a motorized friction wheel are provided for the trolleys,these forming or also forming part of a first system for moving thetrolleys.

This is for example illustrated by way of example in the form of asingle motorized friction traction device 70 in FIG. 1. These systemsmay, however, may be more than one in number, being distributed alongthe conveying line so that they are able to pass in sequence from onetrolley to another trolley along the conveying line (as for exampleshown schematically in FIG. 8). Along the sections where the trolley ismoved by these devices 70 and/or by the additional traction system 60,the conveying line 13 may be advantageously of the passive type, namelywithout a drive system or with the drive system deactivated. Forexample, along these sections the conveying line 13 may be composed ofidle rollers and/or by sliding surfaces.

The traction device 70 which pushes the additional traction systemtowards the engagement point may be easily switched off once engagementof the traction system has been completed (i.e. with at least one toothengaged) so that the traction of the trolley is transferred from thetraction device 70 to the additional traction system. The opposite mayhappen when the action of the additional traction system has terminated,namely when the rack 62 is no longer engaged with the toothed tractionwheel 61.

In order to activate and deactivate the traction devices 70 at the rightmoment, operation thereof is also advantageously controlled by thecontrol circuit 65 which, via the sensor 64, detects the start and theend (or the nearing of the end) of engagement of the additional tractionsystem. Alternatively, the devices 70 may continue to operate so thattheir action is added to that of the wheel 61, even though this maycomplicate the system for controlling the speeds of the two systems suchthat they are uniform with each other.

As shown for example in FIGS. 1 and 3, the traction device 70 maycomprise a gear motor 71 which operates a wheel 72 which rests on asuitable surface of the passing trolley. Advantageously, the wheel 72may be pushed against this surface with a suitable pressure by means ofa resilient thrusting system 73, for example of the spring type. As canbe clearly seen for example in FIG. 3, the surface of the trolley onwhich the wheel 72 rests for movement of the trolley may be a suitablesurface 74 parallel and close to the traction rack 62. In order toensure that the trolley remains on the conveying line without beinglifted laterally despite the forces acting on it for conveying androtation along the plant 10, idle wheels 75 may be provided at intervalsin suitable positions, these resting vertically on top of suitablesliding surfaces of the trolley. As shown in FIG. 4, these surfaces maybe for example the same surface 74 for supporting the motorized wheel72.

Preferably, the idle wheels 75 may be pushed against the correspondingsurfaces of the trolley by means of a resilient thrusting system 76, forexample of the spring type, for providing an adequate vertical pressure.

As is clear from the figures, the devices for rotating the bodywork, thetractions wheel 61 with the associated motor, any friction tractiondevices 70 and any idle wheels 75 may be advantageously all arranged onthe same side of the trolleys and preferably outside of the verticalplane of the basins so as to simplify the structure and the maintenanceof the plant. in particular, the additional traction devices formed bythe wheel 61 and the associated motor 66, the friction traction devices70 and any idle wheels 75 may be suspended from a fixed frame 77arranged on one side of the conveying line. This frame 77 mayadvantageously comprise uprights which are generally in the form of anoverturned L and horizontal beams and may also define a space forallowing the rotation wheel 23 and the associated actuating devices 32to pass through, as is clearly visible in FIGS. 2, 3 and 4.

The devices 70 may be present only at the inlet, only at the outlet, atboth the inlet and outlet, or may be not present at all, depending onthe requirements and structure of the conveying system, as may now beeasily understood by the person skilled in the art on the basis of thedescription provided hitherto.

FIGS. 5, 6 and 7 show by way of example various operating steps in aplant according to the invention. In particular FIG. 5 shows a trolleyduring its approach movement towards the rotation system after theadditional traction system has been engaged. This FIG. 5 also shows inbroken lines the possible existence of a device 70 for pushing theincoming trolley towards the engagement point of the additional movementsystem and in solid lines a device 70 for pulling the trolley out fromthe engagement point of the additional movement system. FIG. 6 shows theaction of the rotation system which rotates the bodywork so as tooverturn it and immerse in an underlying basin 15.

As is now clear to the person skilled in the art, the length of therotation rack may be determined so as to produce any desired angle ofrotation, also by combining it with the transmission ratio chosen forthe transmission of the movement between the rotation wheel 23 and theshaft 19. For example, the angle of rotation of the shaft 19 formed bysliding of the rotation wheel along the entire rotation rack may besuitably chosen as fractions within the range of 0° to 360°, dependingon the requirements of the treatment process and/or the number of teeth(rollers) of the racks. For example, the rotation may be in the regionof 180° or in the region of 360°. The angle of rotation may also bechosen so as to keep the bodywork at a small angle when entering and/orexiting the rotation system, depending also on the requirements of thetreatment process.

FIG. 7 also shows in schematic form a possible design of the plant whichallows the bodywork to he overturned and to remain immersed in theoverturned position until the next rotation system is reached and thebodywork on the trolley is brought back upright. In this case, in theoverturned condition of the bodywork, the action of the additionaltraction system may no longer be necessary. As can be seen in FIG. 7,both engagement of the traction system and engagement of the rotationsystem may therefore terminate after the overturning operation and thetrolley may advance by means of the action of the transportation systemformed by the conveying line and/or any devices 70.

In this way, the bodywork may remain immersed inside the basin (designedwith a suitable lengthwise dimension) along a predetermined section ofthe conveying line and for a predetermined duration. A followingrotation system with an associated additional traction system such asthose described above and shown in FIG. 1 may then bring the bodyworkout of the basin.

All of this is shown schematically in FIG. 8 which shows, in sequence,two rotation systems 10 a and 10 b of a plant 10 according to theinvention, the first one of which turns the bodywork over inside thebasin and the second one of which (which may be at any distance from thefirst one, depending on the bodywork immersion requirements) brings thebodywork back into the normal transportation position.

As can he seen in FIG. 8, at the start of a long basin a rotation rackhaving a length such as to produce a half rotation of the shaft may beprovided, so as to overturn completely the bodywork and immerse itcompletely inside the basin. The trolley may then proceed along thebasin with the bodywork immersed. At the end of the basin a secondrotation rack may be provided, said rack having a length such as toproduce another half rotation of the shaft so as to completely raise thebodywork into the normal advancing position (which is not necessarilyhorizontal but also depends on the transportation requirements and/orthe treatment process and in which the bodywork may also be inclined).

Alternatively, for example in the case of short basins, a singlerotation rack may be obviously designed with a length such as to causethe bodywork to perform a full rotation during the advancing movement ofthe trolley.

If necessary, the trolley may also be stopped when the bodywork is fullyimmersed, such as to cause it to remain in the liquid for the entireduration needed for the particular treatment. It is also possible toconsider making the bodywork perform several immersion and emersionrotations, by means of a suitable longer rack or several racks insequence, or perform only partial overturning operations, for example inorder to keep the immersed or partially immersed bodywork inclined, soas to allow evacuation of the air bubbles.

Obviously, when necessary the engagement of the additional tractionsystem 60 will also be provided so as to ensure the necessary additionalthrusting action for moving the trolleys. At this point it is clear tothe person skilled in the art how it is possible to combine the variousparts of the plant according to the invention in order to obtain desiredprogressions of the bodywork along the line, with great ease andflexibility.

Obviously, the above description of an embodiment applying theinnovative principles of the present invention is provided by way ofexample of these innovative principles and must therefore not beregarded as limiting the scope of the rights claimed herein.

For example, especially along the sections which do not coincide withtreatment basins, the transportation system may be of any known type,for example of the type with traction from below using interconnectedmotorized rollers, etc. It is also possible to easily imagine how thevarious embodiments and the various devices described may be combinedwith each other in any number in order to perform treatments which arecomplex and/or with immersion of a bodywork in successive treatmentbasins.

As mentioned above, the conveying line may also be designed with systemsdifferent from the motorized rollers on which the skids rest and travel.For example, other systems, such as linear motors or friction rollers,etc., may be used, as may be now easily imagined by the person skilledin the art on the basis of the description provided above.

Known systems for causing oscillation of the immersed bodywork in orderto facilitate for example the evacuation of air bubbles may also beprovided. These known systems may act for example on the shaft 19 duringthe forwards movement of the trolley with the bodywork immersed and theshaft 19 released.

For example the overturning systems and the structure of the trolleysmay be different from those shown, For example, as already mentionedabove, the trolley may have an H-shaped structure in plan view with twoside members provided with runners or wheels. The sections of the plantwhich require the additional traction according to the present inventionmay also be different from those shown here by way of example, theadditional traction system being able to be used along other sectionswhere the force for movement of the trolley requires the additionaltraction provided by the system 60.

1. A plant for treatment of bodyworks, the plant comprising: at leastone trolley configured to support a bodywork to be treated; a conveyingline configured to transport the at least one trolley along the plant, afirst system configured to move the at least one trolley along theconveying line, wherein the at least one trolley comprises a tractionrack extending in a direction of movement of the at least one trolleyalong the conveying line; a second system configured to move the atleast one trolley along the conveying line in at least one zone of theplant, the second system comprising a toothed traction wheel, driven bya motor under control of a control system and configured to engage inthe traction rack upon passage of the at least one trolley into the atleast one zone of the plant so as to move the at least one trolley alonga portion of the conveying line under the control of the control system;and sensors configured to detect angular position of the toothedtraction wheel and approaching movement of the at least one trolleytoward the toothed traction wheel, and connected to the control systemso as to cause engagement between the traction rack and the toothedtraction wheel upon arrival of the at least one trolley.
 2. The plant ofclaim 1, wherein the at least one zone comprises a process liquid basin,wherein the conveying line carries the at least one trolley over theprocess liquid basin, and wherein the plant further comprises devicesfor rotation of the bodywork to be treated on the at least one trolleywhich has arrived above the process liquid basin.
 3. The plant of claim1, wherein the traction rack comprises a sequence of rollers, andwherein the toothed traction wheel is a lobed wheel configured to engagebetween the rollers of the sequence of rollers.
 4. The plant of claim 2,wherein at least in a part of the portion of the conveying line wherethe toothed traction wheel is engaged in the traction rack on the atleast one trolley, there are means for actuating devices for rotation ofthe bodywork to be treated on the at least one trolley.
 5. The plant ofclaim 4, wherein the at least one trolley comprises a base part forsupport and movement along the conveying line and a support part forsupporting the bodywork to be treated, wherein the support part isrotatably supported on the base part using a rotatable shaft so that thesupport part can be rotated between a first upper position and a secondposition for immersing the bodywork to be treated in the process liquidbasin, wherein the devices for rotation of the bodywork to be treatedcomprise a toothed rotation wheel which is kinematically connected tothe rotatable shaft, and wherein the actuating means comprises arotation actuating device provided with a rotation rack which isdesigned to engage the toothed rotation wheel to actuate the rotation ofthe support part of the at least one trolley using movement of the atleast one trolley along the rotation rack.
 6. The plant of claim 5,wherein the rotation actuation device is movable controllably between anoperating position and a non-operating position, respectively, forengagement and non-interference with the toothed rotation wheel duringthe movement of the at least one trolley along the rotation rack.
 7. Theplant of claim 5, wherein the at least one trolley comprises acontrollable device for locking/unlocking free rotation of the rotatableshaft.
 8. The plant of claim 7, wherein the controllable device forlocking/unlocking the free rotation of the rotatable shaft is amechanical device controlled to perform unlocking using interferencewith release surfaces arranged along the conveying line.
 9. The plant ofclaim 1, wherein the first system comprises friction traction devicesalong the conveying line which comprise a motorized wheel configured tocontact a corresponding surface of the at least one trolley so as tomove the at least one trolley along the conveying line under the controlof the control system.
 10. The plant of claim 9, wherein the frictiontraction devices are arranged along the conveying line so as to move theat least one trolley along the conveying line at least into a vicinityof a point for engagement and/or disengagement of the toothed tractionwheel with the traction rack.
 11. The plant of claim 1, wherein idlewheels are arranged at intervals along the conveying line, and whereinthe idle wheels rest vertically on top of corresponding sliding surfacesof the at least one trolley.
 12. The plant of claim 11, furthercomprising: means for actuating devices for rotation of the bodywork tohe treated on the at least one trolley; and friction traction devices;wherein the toothed traction wheel, the means for actuating the devicesfor rotation of the bodywork to be treated on the at least one trolley,the friction traction devices, and the idle wheels are arranged on asame side of the at least one trolley along the conveying line.
 13. Amethod for providing additional traction to at least one trolleyconfigured to support a bodywork to be treated along a conveying line ina plant for treatment of bodyworks, the method comprising: providing onthe at least one trolley a traction rack extending in a direction ofmovement of the at least one trolley along the conveying line; arrangingin at least one zone along the conveying line a toothed traction wheelwhich is driven by a motor controlled by a control system and which isconfigured to engage in the traction rack when the at least one trolleypasses into the at least one zone so as to move the at least one trolleyalong a portion of the conveying line under the control of the controlsystem; arranging sensors configured to detect angular position of thetoothed traction wheel and approaching movement of the at least onetrolley toward the toothed traction wheel, and connected to the controlsystem of the toothed traction wheel; detecting the angular position ofthe toothed traction wheel and, when the toothed traction wheel is notengaged in the traction rack, driving the motor so as to bring thetoothed traction wheel into a position suitable for subsequentengagement with the traction rack of the at least one trolley; detectingarrival of the at least one trolley and starting the motor with apredetermined acceleration ramp when a front end of the traction rackapproaches the toothed traction wheel until the toothed traction wheeland the traction rack are engaged, and driving the motor so as tocontinue rotation of the toothed traction wheel for a pushing action ofthe at least one trolley along the conveying line using the tractionrack engaged in the toothed traction wheel.,
 14. The method of claim 13,further comprising: arranging, along the conveying line, frictiontraction devices which have at least one motorized wheel configured tocontact a corresponding surface of the at least one trolley so as tomove the at least one trolley along the conveying line; and actuatingthe friction traction devices so as to move the at least one trolleyalong the conveying line at least into a vicinity of a point forengagement and/or disengagement of the toothed traction with/from thetraction rack.
 15. A plant for treatment of bodyworks, the plantcomprising: at least one trolley configured to support a bodywork to betreated; a conveying line configured to transport the at least onetrolley along the plant; a first system configured to move the at leastone trolley along the conveying line; a second system configured to movethe at least one trolley along the conveying line, the second systemcomprising a toothed traction wheel, motor, and control system; a firstsensor configured to detect angular position of the toothed tractionwheel; and a second sensor configured to detect approaching movement ofthe at least one trolley toward the toothed traction wheel; wherein theat least one trolley comprises a traction rack extending in a directionof movement of the at least one trolley along the conveying line in atleast one zone of the plant, wherein the toothed traction wheel isdriven by the motor under control of the control system, wherein thetoothed traction wheel is configured to engage the traction rack uponpassage of the at least one trolley into the at least one zone of theplant so as to move the at least one trolley along a portion of theconveying line under the control of the control system, and wherein thefirst and second sensors are connected to the control system so as tocause engagement between the toothed traction wheel and the tractionrack upon arrival of the at least one trolley.
 16. The plant of claim15, further comprising: a process liquid basin; and a device configuredto rotate the bodywork to be treated on the at least one trolley whenthe at least one trolley is above the process liquid basin; wherein theconveying line is configured to carry the at least one trolley over theprocess liquid basin.
 17. The plant of claim 15, further comprising: aprocess liquid basin in the at least one zone of the plant; and a deviceconfigured to rotate the bodywork to be treated on the at least onetrolley when the at least one trolley is in the at least one zone of theplant; wherein the conveying line is configured to carry the at leastone trolley over the process liquid basin.
 18. The plant of claim 15,wherein the traction rack comprises a sequence of rollers, and whereinthe toothed traction wheel is a lobed wheel configured to engage betweenthe rollers of the sequence of rollers.
 19. The plant of claim 15,wherein the at least one trolley comprises: a base part for support andmovement along the conveying line; and a support part configured tosupport the bodywork to be treated; wherein the support part isrotatably supported on the base part using a rotatable shaft, andwherein the support part is configured to rotate between a firstposition above the conveying line and a second position below theconveying line.
 20. The plant of claim 15, wherein the at least onetrolley comprises: a base part for support and movement along theconveying line; and a support part configured to support the bodywork tobe treated; wherein the support part is rotatably supported on the basepart using a rotatable shaft, and wherein the support part is configuredto rotate between a first position, in which the bodywork to be treatedis not immersed in a process liquid basin, and a second position, inwhich the bodywork to be treated is at least partially immersed in theprocess liquid basin.